The present invention relates to a fluorescence detection type electrophoresis apparatus, particularly to a multicolor fluorescence detection type electrophoresis apparatus. More specifically, the present invention relates to the multicolor fluorescence detection type electrophoresis apparatus, preferably for determining DNA base sequence of DNA or the like in a way that a plurality of fluorophores of different emission wavelengths are used to label in multicolor the fragments of the DNA or the like to be determined for the base sequences. Each of the fluorescent lights of the DNA fragments emitted after electrophoresis separation then can be detected.
Conventional technique of determining the DNA base sequence is autoradiography in which a radioactive isotope element is used for labeling. However, it is not until recently that a fluorescent label technique is used to optically and automatically detect the DNA fragments to automatically determine the DNA base sequences. This technique uses a method in which four DNA fragments of different terminal species are labeled with respective fluorophores of different emission wavelengths, and the DNA fragments are separated by gel electrophoresis. The DNA fragments are irradiated by laser beam on the migration lanes. The fluorescent lights emitted are received by a detector having four respectively selecting bandpass filters lights of said different emission. A conventional detector of the photomultiplier type having four bandpass filters on a rotary plate is moved synchronously with a scanning laser beam as disclosed for example in "Nature", vol. 321, 1986, pp. 674-679.
There is an alternative technique in which a laser beam is applied on an electrophoretic plate in line and the emitted fluorescent light line image is divided through a prism into spectra, which in turn are detected by a highly sensitive, two-dimensional detector as disclosed, for example, in U.S. Pat. No. 4,832,815.
It is important to achieve a high sensitivity in the fluorescent light detector mentioned above. In the fluorescence measuring system where the detector employing a rotary filter scans with the irradiation scanning beam, the proportion of the measuring time, .alpha., for one measuring point of gel is expressed by EQU .alpha.=d/4l
where l denotes a length of the measuring area, and d denotes a width of the irradiating laser beam. In general, as d is 0.2 to 0.3 mm and l is longer than or equal to 100 mm, .alpha. is smaller than or equal to 10.sup.-3. This is disadvantageous in that it leads to an amount of reception light as low as 1/1000 of the continuous light irradiation and reception method, resulting in a sensitivity that is too low.
On the other hand, in the technique where a laser beam travels through a side end surface of the slab gel to continuously irradiate every measuring point, the fluorescent light images obtained are divided into spectra through a prism, which in turn are detected by a two-dimensional detector. The amount of light reception in this instance is high and resolve the difficulty mentioned above. However, the wavelength dispersion by the prism is not enough to separate lights from different fluorescent dyes. Further, even a slightest position shift of the prism or the lens affect the wavelength separation. That is, a shift of the prism or the lens shifts the position of the image to be detected. Moreover, the light from each fluorescent dye have a wide spectra, although emitted wavelengths from dyes are different only by 20 nm or so at the maximum wavelengths, in many cases. Consequently, it is very difficult to identify different fluorescent dyes, even if the prism is of an optimum quality, and hence, it is difficult to identify with precision the DNA base species using this technique.
As pointed out above, the conventional techniques are disadvantageous in that they lack a high sensitivity and a precision for separating wavelength.